Undercover officer: Mark Kennedy infiltrated the group but the protestors were never told in court

Taxpayers are facing a bill of at least £1 million after the Court of Appeal quashed the convictions of a group of green activists infiltrated by an undercover policeman.

It ruled that the cases against 29 protesters who ambushed a train outside a power station five years ago were unsafe.

Three senior judges said there had been a total failure to disclose evidence from undercover officer Mark Kennedy, but they were unable to rule on whether police, prosecutors or counsel were responsible for the miscarriage of justice.

Those close to the case said the total bill for the police inquiry, prosecution and Court of Appeal proceedings would be ‘at the very least’ £1million.

But another hearing must be held to decide whether West Yorkshire Police, the Crown Prosecution Service or the Ministry of Justice should foot the bill.

In June 2008 a train carrying coal to Drax – Britain’s largest coal-fired power station – near Selby, North Yorkshire, was stopped by two men posing as Network Rail staff.

It was then scaled by protesters who shovelled coal on to the ground and unfurled banners during a 16-hour stand-off.

The activists were convicted at Leeds Crown Court of obstructing engines on railways, an offence under the Malicious Damage Act of 1861. Some were ordered to do 60 hours of unpaid work and others were given 12-month conditional discharges.

Yesterday, the Lord Chief Justice, Lord Thomas, quashed their convictions after the authorities admitted the involvement of Mr Kennedy was hidden.

The ‘complete and total failure’ to disclose evidence fundamental to the activists’ defence meant ‘this court has no alternative but to quash the convictions’.

Earlier, Brian Altman QC, for the prosecution, said the failure to disclose Mr Kennedy’s role had been catastrophic. The police spy, who was also known as Mark ‘Flash’ Stone, infiltrated environmental groups across Europe for more than seven years.

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He attended a private meeting where the campaigners planned their protest, hired a van and drove some of them there.

He kept a detailed record of what happened and made reports to his handler, who passed the information to senior West Yorkshire Police officers.

Result: Protesters (from left) Bryn Hoskins, Beth Stratford and Robbie Gillett, leaving the High Court in London yesterday are among the 29 whose convictions for ambushing a freight train were quashed

Up in smoke: The convictions followed a protest when campaigners ambushed a freight train as it took fuel to Drax, the largest coal-fired power station in Europe (file picture), near Selby in North Yorkshire

If his activities had been exposed, Mr Kennedy would have been accused of acting as an agent provocateur because no one else had a vehicle to get to the protest.

He was exposed in 2010 after documents revealing his true identity were found by chance. He turned on his former employers in the police and apologised to his targets.

Announcement: Former director of public prosecutions Keir Starmer said in 2012 that there were concerns about the safety of the convictions

Robbie Gillett, one of the cleared campaigners, said after the hearing that the case was ‘an invasion of people’s lives, a waste of public money and, from the police’s perspective, a legal failure’.

Lord Thomas asked counsel to prepare written submissions on the question of who should be responsible for the ‘substantial’ legal costs incurred, to be decided at a later date.

Querying why the Ministry of Justice should foot the bill, he commented: ‘This is a plain case of fault, either by the West Yorkshire Police or the CPS, so why shouldn't they pay?’

The defendants, who joined the protest from all over the country, told jurors they did not believe they were doing anything criminal because they were trying to prevent climate change.

The Court of Appeal hearing came after an announcement in 2012 by the then director of public prosecutions Keir Starmer that there were concerns about the safety of the convictions. He those convicted to appeal.

Outside court, Beth Stratford,
speaking on behalf of the 29, said: ‘We are pleased because this shines a
light on the underhand tactics of the police and the Crown Prosecution
Service (CPS) in their policing of political movements.

'It underlines
further the need for public independent inquiry into the use of
political policing.’

John Sauven, executive director of Greenpeace, added: ‘The sheer scale of covert policing against legitimate organisations is corrosive to the democratic values and principles we hold dear.

‘I join with others including Neville and Doreen Lawrence to demand that the Government hold an independent judge-led inquiry into who was responsible for instructing these officers to spy on peaceful, legitimate organisations.’

Other protest two years earlier: Environmentalists camp in the shadow of Drax power station in August 2006